"Multiple-step OLE DB operation generated errors" in pgAdmin II:frmSQLOutput.LoadGrid

I am getting the error message

"Error in pgAdmin II:frmSQLOutput.LoadGrid: -2147217887 - Multiple-step OLE
DB operation generated errors. Check each OLE DB status value, if available.
No work was done."

when trying to do a basic query (select * from staff, or click the button
that has the same effect) on a table with the following definition:

CREATE TABLE "staff" (
  "sid" int4 DEFAULT nextval('"staff_sid_seq"'::text) NOT NULL,
  "lastname" varchar(128),
  "firstname" varchar(128),
  "preferred_contact_method" int4,
  "initials" varchar(32),
  "title" varchar(64),
  "dob" date,
  "emergency_contact_name" varchar(256),
  "e_c_relationship" varchar(256),
  "e_c_address_1" varchar(256),
  "e_c_address_2" varchar(256),
  "e_c_city" varchar(256),
  "e_c_phone_day" varchar(256),
  "e_c_phone_eve" varchar(256),
  "e_c_phone_mob" varchar(256),
  "e_c_email" varchar(256),
  "sex" varchar(6),
  "food_hygene_cert" bool,
  "food_hygene_cert_expiry_date" date,
  "first_aid_cert" bool,
  "first_aid_cert_expiry_date" date,
  "pgp_member" bool,
  "pgp_member_from" date,
  "smoker" bool,
  "medical_notes" text,
  "general_notes" text,
  "tech_experience" int4,
  "house_experience" int4,
  "cafe_experience" int4,
  "inactive" bool,
  "e_c_county" varchar(128),
  "e_c_post_code" varchar(64),
  "e_c_country" varchar(128),
  CONSTRAINT "staff_pkey" PRIMARY KEY ("sid")
) WITH OIDS;
REVOKE ALL ON "staff" FROM PUBLIC;
GRANT ALL ON "staff" TO "user1";
GRANT ALL ON "staff" TO "user2";

Here is the pgadmin (1.20) log at logging level "debug".

21/06/2002 22:42:48 - Counting Records...
21/06/2002 22:42:48 - SQL (PGP_Staff): SELECT count(*) AS count FROM "staff"
21/06/2002 22:42:48 - Done - 0.05 Secs.
21/06/2002 22:42:48 - Executing SQL Query...
21/06/2002 22:42:49 - SQL (PGP_Staff): SELECT * FROM "staff"
21/06/2002 22:42:49 - Loading Data...
21/06/2002 22:42:49 - Done - 0.5 Secs.
21/06/2002 22:42:49 - Error in pgAdmin
II:frmSQLOutput.LoadGrid: -2147217887 - Multiple-step OLE DB operation
generated errors. Check each OLE DB status value, if available. No work was
done.

There are 115 records in the "staff" table. After the error is reported a
display grid comes up, with 70-odd records displayed. I was able to view
this table before I had as many records. Running the query within psql on
the server causes no problems.

Any suggestions?
--
Thomas Sandford